Electrical Connector, Electrical Connection System and Lithographic Apparatus

ABSTRACT

An electrical connector comprises a high voltage pad and a high voltage plate. When connected to another electrical connector, the two plates, which are at the same voltage as the pads, form a region of high voltage in which the field is low. The pads are positioned in that region. An electrostatic clamp of an EUV lithographic apparatus may have such a pad and plate, for connecting to the electrical connector. By placing the interconnection in a low field region, triple points (points of contact between a conductor, a solid insulator and a gas) may be present in that region.

CROSS REFERENCE TO RELATED APPLICATIONS

This applications claims benefit under 35 U.S.C. 119(e) to U.S.Provisional patent Application No. 61/365,554, filed, Jul. 19, 2010,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a high voltage electricalconnector, a high voltage electrical connection system and alithographic apparatus.

2. Background Art

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,including part of, one, or several dies) on a substrate (e.g., a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from a patterning device to the substrate byimprinting the pattern onto the substrate.

A component of the lithography apparatus is powered by a high voltagepower supply. An electrical connector and an electrical connectionsystem are needed that can withstand such high voltage. Furthermore, thecomponent must be able to withstand the high voltage. In a lithographicapparatus, a high voltage power supply may be used to power an actuator,a blade or a clamp, for example. An actuator may be used to position thetable on which the substrate is placed. An actuator may power a bladethat is configured to block a portion of the projection beam. Clampshold the mask or the substrate to a table. One example of a clamp is anelectrostatic clamp, which includes electrodes that are connected to apower supply.

Additionally, for applications other than in lithographic apparatuses,it is desirable to have an electrical connector and an electricalconnection system that can withstand high voltage. Electrical breakdownat high voltage can at least cause damage to, and often destroy,electrical components. Electrical breakdown poses a health risk. Inparticular, electrical breakdown is an increased risk at points ofwiring or components that are at high voltage and are at least partiallyexposed to gas. This may be the case at the terminal of wiring or of acomponent, for example.

If a breakdown occurs, it can damage optical surfaces, createelectromagnetic interference that disturbs sensitive electronics andpresent a human safety hazard. Electrical discharge may causedeterioration of any insulation material of an electrical power line.This may reduce the lifetime of the electrical power line. Electricaldischarge may give rise to unwanted effects such as electromagneticinterference. Such electromagnetic interference may have a negativeinfluence on electronic circuits and/or may violate legislation ofindustry standards.

It is desirable to provide an electrical connector, an electricalconnection system and a lithographic apparatus with an electricalcomponent that can withstand high voltages.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided ahigh voltage electrical connector comprising a laminate that comprises,in order, the following layers:

an outer shield layer;

an outer insulating layer;

a high voltage plate;

an inner insulating layer; and

a high voltage supply pad;

wherein the pad is smaller than the plate and lies substantially whollywithin the plate when viewed in a direction perpendicular to a plane ofthe laminate.

According to a further aspect of the present invention, there isprovided a lithographic apparatus arranged to transfer a pattern onto asubstrate comprising:

an electrostatic clamp configured to clamp a substrate to a structure,the clamp comprising:

-   -   a high voltage receipt pad configured to electrically connect to        a component external to the clamp; and    -   a high voltage plate substantially parallel to the pad;        wherein the pad is smaller than the plate and lies substantially        wholly within the plate when viewed in a direction perpendicular        to a plane of the plate.

According to a further aspect of the present invention, there isprovided a high voltage electrical connection system comprising:

a high voltage supplying electrical connector having a high voltagesupply pad; and

a high voltage receiving electrical component having a high voltagereceipt pad in electrical connection with the supply pad;

wherein a perimeter of both the supply pad and the receipt pad arepositioned in a region that is substantially an equipotential when thesupply pad and the receipt pad are at high voltage.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

Embodiments of different aspects of the present invention will now bedescribed, by way of example only, with reference to the accompanyingschematic drawings, in which corresponding reference symbols indicatecorresponding parts, wherein:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 depicts a schematic view of a high voltage electrical connectionsystem according to an embodiment of the invention;

FIG. 3 depicts a schematic view of a planar electrical connectorsaccording to an embodiment of the invention;

FIG. 4 depicts a schematic view of a planar electrical connectoraccording to one embodiment of the invention;

FIG. 5 depicts a schematic view of a planar electrical connectoraccording to one embodiment of the invention;

FIG. 6 depicts an electrical connection system connecting two electricalconnectors according to an embodiment of the invention;

FIG. 7 depicts an electrostatic clamp connected to a power supplyaccording to an embodiment of the invention;

FIG. 8 depicts a beam interceptor connected to a power supply accordingto an embodiment of the invention;

FIG. 9 depicts a plan view of the electric field map around a plate ofan electrical connector according to an embodiment of the invention;

FIG. 10 depicts a plan view of the electric field map around a plate ofan electrical connector according to an embodiment of the invention;

FIG. 11 and FIG. 12 depict an electrical connector 60 according to anembodiment of the invention electrically connected to an elongateelectrical connector 112;

FIG. 13 depicts a plan view of an electrical connector 60;

FIG. 14 depicts a cross-sectional view of the electrical connector 60depicted in

FIG. 13;

FIG. 15 depicts an electrical connector 60 in plan view;

FIG. 16 depicts the electrical connector 60 of FIG. 15 incross-sectional view;

FIG. 17 depicts in plan view an electrical connector 60 according to anembodiment;

FIG. 18 depicts in plan view an electrical connector 60 according to anembodiment;

FIG. 19 depicts in plan view an electrical connector 60 according to anembodiment;

FIG. 20 depicts in plan view an electrical connector 60 according to anembodiment;

FIG. 21 depicts in plan view an electrical connector 60 according to anembodiment; and

FIG. 22 depicts in plan view an electrical connector 60 according to anembodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus includes:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g., UV radiation or EUV radiation);

a support structure (e.g., a mask table) MT constructed to support apatterning device (e.g., a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g., a wafer table) WT constructed to hold asubstrate (e.g., a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g., a refractive projection lens system) PSconfigured to project a pattern imparted to radiation beam B bypatterning device MA onto a target portion C (e.g., including one ormore dies) of substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e., bears the weight of, thepatterning device. It holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam, which is-reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system-”.

As here depicted, the apparatus is of a reflective type (e.g., employinga reflective mask). Alternatively, the apparatus may be of atransmissive type (e.g., employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

The lithographic apparatus may also be of a type wherein at least aportion of the substrate may be covered by a liquid having a relativelyhigh refractive index, e.g., water, so as to fill a space between theprojection system and the substrate. An immersion liquid may also beapplied to other spaces in the lithographic apparatus, for example,between the mask and the projection system. Immersion techniques arewell known in the art for increasing the numerical aperture ofprojection systems. The term “immersion” as used herein does not meanthat a structure, such as a substrate, must be submerged in liquid, butrather only means that liquid is located between the projection systemand the substrate during exposure.

Referring to FIG. 1, illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from source SOto illuminator IL with the aid of a beam delivery system BD including,for example, suitable directing mirrors and/or a beam expander. In othercases the source may be an integral part of the lithographic apparatus,for example when the source is a mercury lamp. Source SO and illuminatorIL, together with beam delivery system BD if required, may be referredto as a radiation system.

Illuminator IL may include an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, illuminator IL may includevarious other components, such as an integrator IN and a condenser CO.The illuminator may be used to condition the radiation beam, to have adesired uniformity and intensity distribution in its cross-section.

A masking device, which defines the area on the patterning means that isilluminated, may be included in illuminator IL. The masking device mayinclude a plurality of blades, for example four, whose positions arecontrollable, e.g., by actuators such as stepper motors, so that thecross-section of the beam may be defined. It should be noted that themasking device need not be positioned proximate the patterning means butin general will be located in a plane that is imaged onto the patterningmeans (a conjugate plane of the patterning means). The open area of themasking means defines the area on the patterning means that isilluminated but may not be exactly the same as that area, e.g., if theintervening optics have a magnification different than 1.

According to an embodiment of the invention, the masking device includesa beam interceptor 210, including opaque blades 211, 212, 213, 214 thatare arranged to intercept part of radiation beam B, as is shown in FIG.8. Blades 211, 212, 213, 214 manipulate the size and shape of theexposed projection beam B on mask MA and accordingly on target portionsC. The movement and positioning of blades 211, 212, 213, 214 iscontrolled by a control system 220. It a projected target portion C isnot fully positioned on substrate W, control system 220 is arranged todefine a new size for this particular target portion C and actuate beaminterceptor 210 accordingly.

The patterning device (e.g., mask MA) is held on the support structure(e.g., mask table MT) and is patterned by the patterning device. Mask MAcan be clamped to mask table MT on both surfaces of the mask. Byclamping mask MA on both surfaces, the mask can be subjected to largeaccelerations without slipping or deformation. The clamping, or holdingforce may be applied using thin membranes, which further preventdeformation of the mask. By the clamp, a normal force between adjacentsurfaces of the mask and mask table MT is generated, resulting in afriction between contacting surfaces of the mask and the mask table. Theclamping force to the surfaces of mask MA may be generated usingelectrostatic or mechanical clamping techniques.

In EUV lithographic processes, electrostatic clamps may be used to clampmask MA to mask table MT and/or substrate W to substrate table WT. FIG.7 depicts an exemplary electrostatic clamp that is connected to a powersupply 20 via an electrical connector 60 according to an embodiment ofthe present invention. In the exemplary electrostatic clamp 80 depictedin FIG. 7, a chuck 84 includes a dielectric or slightly conductive bodywith an embedded electrode 83. Power supply 20 is used to apply apotential difference between mask MA or substrate W and chuck 84 andbetween chuck 84 and table MT, WT so that electrostatic forces clampmask MA or substrate W and chuck 84 to the table MT, WT. Embeddedelectrode 83 is connected to power supply 20.

Radiation beam B is incident on the patterning device (e.g., mask MA).Having traversed mask MA, radiation beam B passes through projectionsystem PS, which focuses the beam onto a target portion C of substrateW. With the aid of the second positioner PW and position sensor IF2(e.g., an interferometric device, linear encoder or capacitive sensor),substrate table WT can be moved accurately, e.g., so as to positiondifferent target portions C in the path of radiation beam B. Similarly,first positioner PM and another position sensor IF1 can be used toaccurately position mask MA with respect to the path of radiation beamB, e.g., after mechanical retrieval from a mask library, or during ascan. In general, movement of mask table MT may be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of first positioner PM. Similarly,movement of substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of second positionerPW. In the case of a stepper (as opposed to a scanner) mask table MT maybe connected to a short-stroke actuator only, or may be fixed. Mask MAand substrate W may be aligned using mask alignment marks M1, M2 andsubstrate alignment marks P1, P2. Although the substrate alignment marksas illustrated occupy dedicated target portions, they may be located inspaces between target portions (these are known as scribe-lane alignmentmarks). Similarly, in situations in which more than one die is providedon mask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

In step mode, mask table MT and substrate table WT are kept essentiallystationary, while an entire pattern imparted to the radiation beam isprojected onto a target portion C at one time (i.e., a single staticexposure). Substrate table WT is then shifted in the X and/or Ydirection so that a different target portion C can be exposed. In stepmode, the maximum size of the exposure field limits the size of thetarget portion C imaged in a single static exposure.

In scan mode, mask table MT and substrate table WT are scannedsynchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e., a single dynamic exposure). Thevelocity and direction of substrate table WT relative to mask table MTmay be determined by the (de-)magnification and image reversalcharacteristics of projection system PS. In scan mode, the maximum sizeof the exposure field limits the width (in the non-scanning direction)of the target portion in a single dynamic exposure, whereas the lengthof the scanning motion determines the height (in the scanning direction)of the'target portion.

In another mode, mask table MT is kept essentially stationary holding aprogrammable patterning device, and substrate table WT is moved orscanned while a pattern imparted to the radiation beam is projected ontoa target portion C. In this mode, generally a pulsed radiation source isemployed and the programmable patterning device is updated as requiredafter each movement of substrate table WT or in between successiveradiation pulses during a scan. This mode of operation can be readilyapplied to maskless lithography that utilizes programmable patterningdevice, such as a programmable mirror array of a type as referred toabove.

In a lithographic projection apparatus according to the presentinvention, at least one of first object table MT (support structure forsupporting the patterning means, the mask) and second object table WT(the substrate table) are provided in a vacuum chamber VC. The vacuuminside vacuum chamber VC is created with evacuating means VE, forexample a pump.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

First positioner PM, second positioner PW, the motors that control anyblades that may be included in the masking device, and any clamps thatmay be included in the lithographic projection apparatus are powered bya high voltage power supply. In particular, the electrodes of anelectrostatic clamp used for clamping a substrate W to a substrate tableWT or a mask M to a mask table MT in near-vacuum conditions areconnected to a bi-polar high voltage supply.

In a lithographic apparatus that uses extreme ultraviolet light as aradiation source, the path of the EUV radiation beam through thelithographic apparatus is enclosed within a vacuum environment. Here,vacuum is taken to mean a very low pressure, such as less than 100 Pa,or even less than 10 Pa, for example. A very low pressure is used toreduce the amount of EUV radiation that would otherwise be absorbed bythe gas particles.

In such an EUV lithographic apparatus, the substrate and the substratetable are enclosed within a vacuum environment. In order to clamp thesubstrate to the substrate table, instead of a vacuum clamp, anelectrostatic clamp is used. The vacuum clamp is not effective becausethe ambient pressure is too low to provide sufficient force to clamp thesubstrate to the substrate table. An electrostatic clamp may be used ina lithographic apparatus for other purposes, for example to clamp areticle to a reticle stage. The electrostatic clamp requires highvoltage to provide sufficient clamping force.

When high voltage is used, the possibility of electrical breakdown isincreased with respect to electrical components that operate at lowervoltages. Here, high voltage is taken to mean a voltage of greater than1 kV, greater than 2 kV, greater than 3 kV, greater than 5 kV or evengreater than 10 kV. Electrical breakdown at high voltage can at leastcause damage to, and often destroy, electrical components.

Electrical breakdown poses a health risk. In particular, electricalbreakdown is an increased risk at points of wiring or components thatare at high voltage and are at least partially exposed to gas. This maybe the case at the terminal of wiring or of a component, for example. Itis desirable to provide an electrical connector, an electricalconnection system and a lithographic apparatus with an electricalcomponent that can withstand high voltages.

The lithographic apparatus may comprise an electrostatic clamp 80, asillustrated in FIG. 7. The electrostatic clamp 80 is connected to a highvoltage power supply 20 by at least one electrical connector 60. Theinterconnection between the electrical connector 60 and theelectrostatic clamp 80 is an electrical connection system 90, asillustrated in FIG. 2. If a plurality of electrical connectors 60 areused, then the interconnection between two electrical connectors 60 isan electrical connection system 90. The electrical connector 60 and theelectrical connection system 90 may be used in applications other thanin a lithographic apparatus. The electrical connection system 90 mayconnect any two electrical components, i.e., not necessarily theelectrical connector 60 or electrostatic clamp 80 of the presentinvention.

Specifically, FIG. 2 depicts an electrical connection system 90according to the present invention. The electrical connection system 90comprises a high voltage supply pad 61 and a high voltage receipt pad81. The supply pad 61 and the receipt pad 81 are electrically connectedto each other. The supply pad 61 is a part of an electrical connector60. The receipt pad 81 is a part of an electrical component other thanthe electrical connector 60. The electrical component may be anelectrostatic clamp 80 of a lithographic apparatus. The electricalcomponent may be another electrical connector, equivalent to theelectrical connector 60.

The supply pad 61 and the receipt pad 81 are positioned in a region thatis substantially an equipotential. In the vicinity of the pads 61, 81,the voltage does not vary significantly. The electric field in theregion in which the pads are disposed is low, even when the electricalconnection system 90 is connected to a high voltage. According to thepresent invention, a low electric field may be an electric field of lessthan about 1 kV/mm, less than about 0.5 kV/mm, or preferably less thanor equal to about 0.3 kV/mm. The strength of the electric field shouldbe ensured to be within acceptable tolerances. The acceptable value forthe electric field depends on the dielectric strength of the materialsused to form the electrical connector 60 and electrical component of theelectrical connection system 90.

By positioning the pads 61, 81 in a region that is substantially anequipotential, the possibility of electrical breakdown is reduced. Thesupply pad 61 is a part of the electrical connector 60 that is at leastpartially exposed to the atmosphere. The receipt pad 81 is a part of theelectrical component that is at least partially exposed to theatmosphere. When the supply pad 61 and the receipt pad 81 are broughtinto electrical contact with each other, it is desirable for the supplypad 61 and the receipt pad 81 to be in contact with only solidmaterials. In particular, it is desirable that the pads 61, 81 are incontact with each other, with a conductor that forms a part of theelectrical connector 60 or electrical component, and solid insulatingmaterial. The insulating material may be termed potting material.

In practice it is very difficult to completely cover the whole surfaceof the supply pad 61 and the receipt pad 81. There may be a gas pocket75, which gas comes into contact with a surface of at least one of thesupply pad 61 and the receipt pad 81. The supply pad 61 and the receiptpad 81 may be in contact with a solid material. In particular, the minorsurface of the supply pad 61 may be covered by a supply pad insulator68. The major surface of the supply pad 61 opposite the surface thatfaces the receipt pad 81 may be covered by an inner insulation layer 63.The minor surface of the receipt pad 81 may be covered by a receipt padinsulator 88. The major surface of the receipt pad 81 opposite thesurface that faces the supply pad 61 may be covered by a componentinsulator 89.

A part of the surface of the supply pad 61 and a part of the surface ofthe receipt pad 81 come into contact with both a gas (e.g., the gaspocket 75) and a solid insulator (e.g., the supply pad insulator 68 andthe receipt pad insulator 88). The point at which a conductor (e.g., thepad 61, 81), a gas (e.g., the gas pocket 75) and a solid insulator(e.g., the insulator 68, 88) meet is termed a “triple point”.

At such a triple point, the magnitude of the electric field isincreased. This is because the component of the electric field that isnormal to the surface of the conductor (e.g., the pad 61,81) isamplified. The factor of amplification depends on the dielectricconstant of the gas and of the insulator. For example, if the gas isair, which has a dielectric constant of about 1, and the solid insulatoris a polyimide, which has a dielectric constant of about 3, then theamplification factor for the electric field is about 3×. Hence,electrical breakdown is a particularly pertinent danger at a triplepoint, and a triple point is most likely to occur, albeit undesirably,at the terminals of electrical components.

Field emission of electrons is most likely to occur at a triple point.This can result in ionisation of the gas at the triple point. The gasmay be air, or hydrogen for example. Corona discharge can occur, heatingup the insulator. Solid insulators can break down due to overheating. Apolymer dielectric used as the insulator (i.e., as the supply padinsulator 68 and/or the receipt pad insulator 88) may decompose underthese conditions. A glass used as the insulating material may becomecracked due to the resulting mechanical stress.

Partial electrical discharge can occur at gas bubbles, which may bepresent within the insulator, for example. These gas bubbles may not betriple points because a conducting surface does not come into contactwith the gas and the insulator. Although these gas bubbles areproblematic, the triple points are more problematic.

One way to reduce the possibility of electrical breakdown is to reducethe voltage of the electrical system. However, according to the presentinvention, it is ensured that the terminals in an electrical connectionsystem 90 are positioned at an equipotential such that the electricalfield is low. This reduces the possibility of electrical breakdown whileallowing a high voltage to be used.

One way to ensure that the supply pad 61 and the receipt pad 81 are at aposition of equipotential is to provide a high voltage plate on eitherside of the pads 61, 81. In the electrical connection system 90, theelectrical connector 60 may comprise a high voltage supply plate 62. Theelectrical component 80 may comprise a high voltage receipt plate 82.The high voltage plate 62, 82 is bigger than the corresponding highvoltage pad 61, 81. Preferably, the high voltage plate 62, 82 issubstantially parallel to the corresponding high voltage pad 61, 81.

The supply pad 61 lies substantially wholly within the supply plate 62when viewed in a direction perpendicular to the plane of the supply pad61. The receipt pad 81 lies substantially wholly within the receiptplate 82 when viewed, for example, in a direction perpendicular to theplane of the receipt pad 81, as viewed in this cross-section. The plates62, 82 are at substantially the same voltage as the pads 61, 81. Thepurpose of the plates 62, 82 is to produce a region in which the voltageis high throughout the region. The pads 61, 81 are positioned within theregion.

The pads 61, 81 are positioned substantially wholly within a volume thathas as its edges the plates 62, 82 and surfaces extending between theperimeters of the plates 62, 82.

It is possible that a portion of a high voltage pad 61, 81 of theelectrical connection system 90 does not lie within the correspondinghigh voltage plate 62, 82, provided that the plates produce a region atsubstantially an equipotential. For example, at least one of the highvoltage plates 62, 82 may have a hole or a slit within the plate, atwhich point the corresponding high voltage pad 61, 81 does not overlapthe corresponding plate 62, 82. However, substantially all of the highvoltage pad 61, 81 overlaps the corresponding high voltage plate 62, 82.

The inner insulation layer 63 of the electrical connector 60 isinterposed between the supply pad 61 and the high voltage supply plate62 of the electrical connector 60. The component insulator 89 isinterposed between the receipt pad 81 and the high voltage receipt plate82 of the electrical component. The high voltage plates 62, 82 aresubstantially surrounded by solid materials. In particular, the highvoltage supply plate 62 of the electrical connector is sandwichedbetween the inner insulating layer 63 and an outer insulating layer 64.The purpose of surrounding the plates 62, 82 by solid materials is toprevent the occurrence of triple points at the surface of the plates 62,82.

As mentioned above, the high voltage plate 62, 82 is larger than thecorresponding high voltage pad 61, 81 and is positioned to overlapsubstantially all of the high voltage pad 61, 81. Preferably, theminimum distance of overlap, d, is at least h, where h is the distancebetween the high voltage pad 61, 81 and the corresponding high voltageplate 62, 82. The distance h is measured in a direction perpendicular tothe plane of the pad 61, 81 and corresponding plate 62, 82. The distanceh is the minimum distance between the pad 61, 81 and the correspondingplate 62, 82. The distance h is the thickness of the inner insulatinglayer 63, or the thickness of the component insulator 89. Preferably,the plate 62, 82 overlaps the entire perimeter of the pad 61, 81 by atleast the distance h. If d=h, then the electric field strength at thesurface of the pads 61, 81, is approximately 10-15% of the maximum value(i.e., in the case where no plates 62, 82 were provided). If d=0, thenthe field strength is about 50% of its maximum value.

In an embodiment, the distance of overlap, the minimum distance betweena perimeter of the plate 62, 82 and the perimeter of the correspondingpad 61, 81 is at least 2h, preferably at least 3h, more preferably atleast 4h and even more preferably at least 5h. If d is at least 5h, thenthe field strength is negligibly small.

FIG. 3, FIG. 4 and FIG. 5 depict an electrical connector 60 according tothe present invention. The electrical connector 60 comprises a laminatethat comprises, in order a shield layer 65, an outer insulating layer64, a high voltage supply plate 62, an inner insulating layer 63 and ahigh voltage supply pad 61. The laminate may be flexible. The insulatinglayers 63, 64 are made of an insulating material. The insulatingmaterial may be flexible, such as a polyimide, or the like. Theinsulating material may be inflexible, for example a float glass or analkali-free glass, or the like. The shield 65, the plate 62 and the pad61 are made of an electrically conductive material, such as copper, orthe like. An insulating layer may be positioned on an outside of thelaminate, thereby sandwiching the shield layer 65.

The high voltage supply pad 61 is a terminal of the electrical connector60. The supply pad 61 may be connected electrically to a high voltagesupply pad 61 of another electrical connector 60, or to a high voltagereceipt pad 81 of an electrostatic clamp 80 of a lithographic apparatus,for example. The high voltage supply plate 62, as described above,contributes to the formation of a region of equipotential in which thesupply pad 61 is positioned when the electrical connector 60 is in use.

The relationship between the dimensions of the supply plate 62 and thesupply pad 61 are as described above in relation to the electricalconnection system 90 of the present invention. In particular, where thesame reference numeral of a component is used in different parts of thisdescription, the characteristics, whether inherent or in relation toanother component, of that component described in relation to oneembodiment of the invention are equally applicable to that component inother embodiments of the invention.

The plate 62 is at the same voltage as the supply pad 61 when theelectrical. connector 60 is in use. Preferably, the high voltage supplyplate 62 is integral with a high voltage trace within the same layer ofthe laminate.

FIG. 3 depicts the electrical connector 60 viewed in cross section, thecross section being perpendicular to the longitudinal direction of thehigh voltage trace of the electrical connector 60. The supply pad 61 issurrounded within the plane of the supply pad 61 by a supply padinsulator 68. The supply pad insulator 68 is arranged to cover a minorsurface of the supply pad 61. In practice, it may be difficult to coverthe whole of the minor surface of the supply pad 61 with insulatingmaterial without preventing electrical contact between the supply pad 61and the electrical component to which electrical connection is made. Assuch, a gas bubble 75 may be situated between the supply pad 61 and thesupply pad insulator 68. If electrical breakdown occurs, then the supplypad insulator 68 may get damaged. However, by haying the plate 62 largerthan the supply pad 61 such that the pad 61 lies substantially whollywithin the plate 62 when viewed in a direction perpendicular to theplate 62, the possibility of electrical breakdown is reduced.

Preferably, the electrical connector 60 comprises a supply pad shield 66within the same layer of the laminate as the supply pad 61. The supplypad insulator 68 is interposed between the supply pad 61 and the supplypad shield 66. The shield layer 65 and the supply pad shield 66 areconnected to electrical ground.

The purpose of the shield layer 65 and the supply pad shield 66 is toprevent electrical breakdown by enclosing the electric field between thenigh voltage plate 62 and trace and the shield layer 65, 66. The regionbetween the high voltage plate 62 and trace and the shield layers 65, 66is filled by the inner insulating layer 63 and the outer insulatinglayer 64.

Preferably, the high voltage supply pad 61 is electrically connected tothe high voltage supply plate 62 by at least one high voltage via 70.This allows electrical current to pass through the high voltage trace,through the high voltage supply plate 62, through the high voltage via70 to the high voltage supply pad 61.

FIG. 4 depicts the electrical connector 60 viewed in cross section, thecross section being parallel to the direction of elongation of the highvoltage trace of the electrical connector 60. Within the layer of thelaminate in which the high voltage supply plate 62 is positioned, theplate 62 may be surrounded by a plate insulator 69. The plate issurrounded in a plane of the plate by the dielectric 69 such that theplate is fully surrounded in a cross section of the laminate by solidmaterial. The plate insulator 69 covers a minor surface of the plate 62except for the section of the plate 62 that is extended to form anintegral connection with the high voltage trace. The plate insulator 69is interposed between the plate 62 and a plate shield 67, which isconfigured to be connected to electrical ground. The plate shield 67 iswithin the same layer of the laminate as the plate 62.

Preferably the supply pad shield 66 is connected to the plate shield 67by at least one ground via 71. Preferably, the plate shield 67 isconnected to the ground shield layer 65 by at least one ground via 71.Preferably, the supply pad shield 66 is connected to the ground shieldlayer 65 by at least one ground via 71.

In an alternative embodiment, the plate 62 is not integral with the highvoltage trace but is in a different layer of the laminate. In this case,the plate 62 may be electrically connected to the high voltage trace bya via, or alternatively the plate 62 may be connected to a separate highvoltage supply such that the plate 62 is at substantially the samevoltage as the high voltage supply pad 61.

The insulating material used for any of the insulating layers orsections of insulation of the electrical connector may be made of, forexample, a polyimide, or a float glass, but other known insulators maybe employed. The layers of the laminate may be adhered together using,for example, an epoxy adhesive, an acrylic adhesive or a polyurethaneadhesive.

Preferably, the laminate comprises a triple point insulator 72, whichmay be termed a ground shield insulator, configured to cover the supplypad shield 66. The purpose of the triple point insulator 72 is toprevent the formation of triple points, as described above, at thesurface of the supply pad shield 66. The triple point insulator maycover substantially all of the outward facing surface of the supply padshield 66. The triple point insulator 72 includes a hole at the highvoltage supply pad 61 to allow the supply pad 61 to be electricallyconnected to another electrical component.

FIG. 5 depicts the electrical connector 60 in plan view, with the planeof the paper in the same plane as the laminate. The supply pad insulator68, the supply pad shield 66, the inner insulating layer 63 and thetriple point insulator 72 are not depicted for illustrative reasonsonly. As depicted in FIG. 9, the supply pad 61 is smaller than thesupply plate 62 and lies substantially wholly within the supply plate62.

FIG. 9 depicts an embodiment of the invention in which the plate 62takes the form of a teardrop shape. The teardrop shape may be describedas being formed primarily of two parts. One part 62 a is substantiallycircular, or oval, for example. The substantially circular part 62 aoverlaps substantially all of the supply pad 61. Another part of theteardrop shape is a tapered part 62 b. The tapered part is extended toform a high voltage trace 62 c. The plate 62 does not have to becircular or oval in part. Contour lines in FIG. 9 show the electricfield strength in the region in arbitrary units around the plate 62. Theelectric field is strongest at the end of the high voltage trace and atthe edge of the circular part furthest away from the high voltage trace.

FIG. 10 depicts an embodiment in which the plate 62 has a substantiallycircular shape 62 a with a high voltage trace 62 c extending radiallyfrom the circular shape. Contour lines in FIG. 10 show the electricfield strength in the region surrounding the plate in arbitrary units.As can be seen from FIG. 10, although the plate 62 includes a sharpcorner 62 d, between the circular part 62 a and the high voltage tracepart 62 c, the electric field at this sharp corner is low. As with theshape of the plate depicted in FIG. 9, the electric field is strongestat the extremities of the plate 62, namely at the end of the highvoltage trace and at the edge of the circular part furthest from thehigh voltage trace.

Other shapes, even angular shapes are possible. A rounded shape ispreferable to avoid spikes in the electric field values. The sharpcorner 62 d of the shape of the plate 62 depicted in FIG. 10 is an“internal” corner (i.e., the corner is at a concave point of the shape).Shapes having “external” sharp corners result in high fields at thesharp corners. Similarly for the supply pad 61, the pad 61 may besubstantially circular although the shape is not particularly limited.

A minimum distance between the perimeter of the pad 61 of the connectorand the pad ground shield 66 is within the range of from about 3h toabout 7h, preferably within the range of from about 4h to about 6h, ormore preferably about 5h.

FIG. 6 depicts an electrical connection system 90 of the presentinvention. The electrical connection system 90 is formed between twoelectrical connector 60 of the present invention. The supply pads 61 arein electrical contact with each other. An insulating sheet 73 may beinterposed between the two electrical connectors 60. The sheet 73 may bemade of a fluoropolymer elastomer, for example. Other types ofinsulating material may be used for the sheet 73. A material that has anelastic material is preferable in order to allow the electricalconnectors 60 to be pressed together tightly, minimizing the presence ofgas pockets 75 in the electrical connection system 90. The purpose ofthe sheet 73 is to fill in the gas pocket between the two electricalconnectors 60.

The sheet 73 is pierced by an electrical contact 74. The contact 74 ismade of an electrically conductive material, such as stainless steel orcopper. The contact 74 extends through the sheet 73. The contact 74 maytake the form of a leaf spring such that when the two electricalconnectors 60 are pressed together the contact 74 is in a compressedstate. This helps to produce a secure connection. As depicted in FIG.10, gas pockets may be present between the sheet 73 and the facingsurfaces of the laminates. If the gas pocket 75 is in contact with apart of the supply pad 61, then a triple point is created. The plates62, which are at the same voltage as the pads 61, produce anequipotential region encompassing the pads 61.

The two electrical connectors 60 may be held together in the electricalconnection system 90 by a screw or by a mechanical clamp, for example.These are not depicted in FIG. 6.

FIG. 7 depicts a section of a lithographic apparatus according to anembodiment of the invention. The lithographic apparatus comprises anelectrical component 80. The component 80 comprises a high voltagereceipt pad 81 and a high voltage receipt plate 82. The principal of thecomponent 80 is the same as explained in relation to the electricalconnection system 90 and the electrical connector 60 of the presentinvention. The receipt plate 82 contributes to the formation of a regionof equipotential when the receipt pad 81 is electrically connected to anelectrical connector 60 to form an electrical connection system 90. Thecomponent 80 is connected to a high voltage power supply 20.

The component may be an electrostatic clamp 80, as depicted in FIG. 7.The clamp 80 comprises the receipt pad 81 and the receipt plate 82. Theclamp 80 further comprises a chuck 84 within which at least one clampelectrode 83 is positioned. The clamp electrode is electricallyconnected to the receipt pad 81. The clamp 80 is used, for example, toclamp a substrate W to a substrate table WT of the lithographicapparatus. The receipt pad 81 and the receipt plate 82 may have the samecharacteristics as described in relation to the supply pad 61 and thereceipt mate 62 of the electrical connector 60. In an embodiment, theelectrode 83 acts as the receipt plate 82.

The supply pad 61 may be glued to the receipt pad 81 by an electricallyconductive silver paint. The vicinity of the connection between thesupply pad 61 and the receipt 81 may be potted by an epoxy, acrylic orpolyurethane adhesive. It is possible for a gas bubble to occur withinthe potting. As a result, there may be a triple point at the surface ofthe supply pad 61 and/or at the surface of the receipt pad 81. Bypositioning the pads 61, 81 in a region that is substantially at anequipotential, the possibility of electrical breakdown is reduced.

FIG. 8 depicts a part of a lithographic apparatus according to anembodiment of the invention. The electrical component 80 of thelithographic apparatus is a control system 220 of blades. The controlsystem comprises a high voltage receipt pad 81 and a high voltagereceipt plate 82.

In FIG. 7 and FIG. 8, the electrical component 80 is connected to a highvoltage power supply 20 via an electrical connector 60 according to thepresent invention. FIG. 7 and FIG. 8 are schematic drawings and not toscale. The relative size of the electrical connector 60 may be increasedfor illustrative purposes.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

Although specific reference may have been made above to the use ofembodiments of the invention in the context of optical lithography, itwill be appreciated that the invention may be used in otherapplications, for example imprint lithography, and where the contextallows, is not limited to optical lithography. In imprint lithography,topography in a patterning device defines the pattern created on asubstrate. The topography of the patterning device may be pressed into alayer of resist supplied to the substrate whereupon the resist is curedby applying electromagnetic radiation, heat, pressure or a combinationthereof. The patterning device is moved out of the resist leaving apattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.,having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) andextreme ultra-violet (EUV) radiation (e.g., having a wavelength in therange of 5-20 nm), as well as particle beams, such as ion beams orelectron beams.

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, includingrefractive, reflective, magnetic, electromagnetic and electrostaticoptical components.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

FIG. 11 and FIG. 12 depict an electrical connector 60 according to anembodiment of the invention electrically connected to an elongateelectrical connector 112. The electrical connector 60 may be theelectrical connector 60 according to any embodiment of the invention.The elongate electrical connector 112 may comprise an electrical wire.The elongate electrical connector 112 may comprise an electrical cable.In an embodiment, the elongate electrical connector 112 comprises acoaxial cable.

In FIG. 11 and FIG. 12, a cross-sectional view of the elongateelectrical connector 112 electrically connected to the electricalconnector 60 is shown. The electrical connector 60 may be planar andflexible. The elongate electrical connector 112 comprises an elongateelectrical conductor. The elongate electrical conductor electricallyconnects to the high voltage supply pad 61 of the electrical connector60. This is depicted in FIG. 11 and FIG. 12.

The elongate electrical conductor may be surrounded in cross-section byan electrical insulator 114, 115. The electrical insulator 114, 115 maybe disposed between the elongate electrical conductor and an outershielding sleeve 116. The elongate electrical conductor may besubstantial coaxial with the shielding sleeve 116. The diameter of theshielding sleeve 116 may be substantially the same as the inner diameterof the supply pad shield 66 that surrounds the supply pad 61.

FIG. 11 depicts an embodiment in which the cross-sectional area of theelongate electrical conductor increases towards the terminal end of theelongate electrical connector 112. The cross-sectional area of theelongate electrical conductor may be substantially the same as the areaof the supply pad 61 of the electrical connector 60. The elongateelectrical conductor may comprise a terminal end in the shape of atrumpet. This may be termed a trumpet end 111. The trumpet end 111 maybe integral to the elongate electrical conductor. The trumpet end 111 isconfigured to electrically connect to the supply pad 61 of theelectrical connector 60. There may be a step change in thecross-sectional area of the elongate electrical conductor at the startof the trumpet end 111.

The elongate electrical conductor may be surround in cross-section by aninner insulator 114. The inner insulator 114 may comprise a fluorocarbonsolid. In an embodiment, the inner insulator 114 comprises PTFE. Theinner insulator 114 may surround the elongate electrical conductor incross-section along substantially the whole of the length of theelongate electrical connector 112 as depicted in FIG. 12. In anembodiment, the inner insulator 114 surrounds substantially the wholelength of the elongate electrical conductor except for the trumpet end111 as depicted in FIG. 11.

The elongate electrical conductor may be surrounded in cross-section byan outer insulator 115. The outer insulator 115 may comprise a syntheticrubber. In an embodiment, the outer insulator 115 comprises afluoroelastomer. As depicted in FIG. 11, the outer insulator 115 maycome into direct contact with the outer surface of the trumpet end 111of the elongate electrical conductor.

The shielding sleeve 116 may come into direct contact with the outersurface of the outer insulator 115. In an embodiment, the terminal endof the trumpet end 111 is substantially flush with the terminal end ofthe outer insulator 115, and optionally the inner insulator 114.

As depicted in FIG. 11, there may be a gas gap at the end of the trumpetend 111 that is integrally connected to the rest of the elongateelectrical conductor. The gas gap may be at the point along the elongateelectrical conductor at which there is a step change in itscross-sectional area. The gas gap may be disposed between the trumpetend 111 and the inner insulator 114.

The gas gap causes a triple point 119 where the gas, the insulators 114,115 and the elongate electrical conductor meet. In particular, thetriple point 119 may be formed at the outer edge of the trumpet end 111of the electrical conductor at which point the outer edge of the trumpetend 111 comes into contact with the outer insulator 115 and the gas inthe gas gap. The presence of the outer insulator 115 amplifies theelectrical field at the triple point 119. The electrical field at thetriple point 119 may be amplified by a factor of approximately ten.

There is accordingly a danger that electrical breakdown may occur due tothe electrical field at the triple point 119. In an embodiment, theouter insulator 115 has sufficiently high insulation properties and isof a sufficient thickness so as to prevent electrical breakdown betweenthe edge of the trumpet end 111 and the inner surface of the shieldingsleeve 116 when the elongate electrical conductor is at high voltage.The shielding sleeve 116 may be connected to electrical ground. In anembodiment, the outer insulator 115 may have a thickness (between theouter edge of the trumpet end 111 and the inner surface of the shieldingsleeve 116) within the range of from about 1 mm to about 6 mm, morepreferably within the range of from about 2.0 mm to about 2.9 mm andpreferably about 2.4 mm.

As depicted in FIG. 11, a triple point 113 may be formed at the outeredge of the supply pad 61. This is because in an embodiment, the triplepoint insulator 72 may not come into contact with the edge of the supplypad 61. As a result, there may be a gas gap between the outer edge ofthe supply pad 61 and the inner surface of the triple point insulator 72surrounding the supply pad 61 even when the electrical connector 60 iselectrically connected via the supply pad 61 to another electricalconnector. The triple point 113 is formed at the outer edge of thesupply pad 61 that comes into contact with the gas in the gap and theouter insulator 115. The gas gap may in fact be a vacuum, or be atsufficiently low pressure as to be considered as substantially a vacuum.Similarly, the gas gap at the inner surface of the trumpet end 111 maybe at a vacuum pressure.

The supply plate 62 has an area such that the triple point 113 fallswithin the area of the supply plate 62 when viewed in the longitudinaldirection of the elongate electrical connector 112. The presence of thesupply plate 62 results in a decrease in the electrical field at thetriple point 113. Hence, the supply plate 62 reduces the possibility ofelectrical breakdown at the triple point 113. Of course, the triplepoint 113 is not within a true no field zone. This is because asexplained in relation to FIG. 2, a true no field zone requires a pair ofplates, whereas the electrical connection shown in FIG. 11 has a singlehigh voltage supply plate 62.

FIG. 12 depicts an embodiment in which the elongate electrical conductordoes not have a trumpet end. The elongate electrical connector 112depicted in FIG. 12 does not have the triple point 119 depicted in FIG.11. This reduces the possibility of electrical breakdown due to thetriple point 119.

However, it is still possible for a triple point to be formed at theouter edge of the supply pad 61. As mentioned above, the presence of thesupply plate 62 can reduce the electrical field at such a triple point113. However, in the case of the electrical connection between theflexible planar electrical connector 60 and the elongate electricalconnector 112, the triple point 113 is not positioned in a no fieldzone.

In an embodiment, the triple point insulator 72 covers the outer edge ofthe supply pad 61. The presence of the triple point insulator 72 acts toeliminate the presence of the triple point 113. This reduces thepossibility of electrical breakdown due to the triple point 113. Thetriple point insulator 72 may extend over a peripheral portion of theexternally facing area of the supply pad 61. The triple point insulator72 comes into direct contact with the outer minor edge of the supply pad61. The triple point insulator 72 covers substantially all of the minoredge of the supply pad 61.

In the embodiment depicted in FIG. 12, which does not have the trumpetend 111 depicted in FIG. 11, the electrical field at any triple point113 at the outer edge of the supply pad 61 may be particularly high.This is because of the geometry of the elongate electrical connector112, which results in a particularly sharp edge at the outer edge of thesupply pad 61 where the triple point 113 may be. Hence, it isparticularly advantageous for the triple point insulator 72 to cover theouter edge of the supply pad 61 when there is no trumpet end 111comprised in the elongate electrical conductor of the elongateelectrical connector 112.

FIG. 13 depicts in plan view an electrical connector 60 according to anembodiment of the invention. FIG. 14 depicts a cross-sectional view ofthe electrical connector 60 depicted in FIG. 13. In FIG. 13, the dashedlines represent the boundary between the supply plate 62 and the plateinsulator 69. The supply plate 62 and the plate insulator 69 aredisposed in the middle layer of the electrical connector 60. Theboundary between the high voltage supply pad 61 and the supply padinsulator 68 is shown in a solid line. The boundary between the supplypad insulator 68 and the supply pad shield 66 is shown as a solid line.

The supply pad insulator 68 is disposed in a region in between the outeredge of the high voltage supply pad 61 and the inner edge 131 of thesupply pad shield 66. The inner edge 131 of the supply pad shield 66surrounds the high voltage supply pad 61 in plan view. Plan view meansthe view in the direction normal to the planes of the laminated layersthat form the electrical connector 60.

The inner edge 131 of the supply pad shield 66 may have a substantiallycircular shape. Other shapes are also possible such as an ellipse, or aquadrilateral, for example.

The supply plate 62 comprises a high voltage trace 62 c that extends inan elongate manner from the substantially circular, or oval, for examplepart 62 a of the supply plate 62. The high voltage trace 62 c extendsfrom part 62 a of the supply plate 62 under the supply pad shield 66. Anouter edge 132 of the high voltage trace 62 c may be substantiallyperpendicular to the inner edge 131 of the supply pad shield 66 at thepoint where the high voltage trace 62 c crosses the inner edge 131 ofthe supply pad shield 66 in plan view. FIG. 13 depicts such anarrangement.

As depicted in FIG. 6, an insulating sheet 73 may be interposed betweentwo electrical connectors 60 so as to block the surface discharge paththat would otherwise be present. This reduces the surface electricaldischarge that would otherwise lead to failure of the insulator bycreating a conductive (e.g., carbonised) path. Although the surfacedischarge path may be at least reduced and possibly neutralised, gaspockets 75 may remain. This is because of the limited flexibility of theinsulating sheet 73. As a result, a triple point can occur at the gaspockets 75.

A triple point in a high electrical field can lead to partial electricaldischarge in the gas pockets thereby eroding the gas pockets bothmechanically and chemically. This is particularly the case when thesystem is subjected to an alternating current, for example in anelectrostatic c′amp system 80. When subjected to an alternating current,a conductive residue can be formed by chemical reactions, resulting inbreakdown of the solid insulator. This can in turn blast away theconstruction by high pressure and temperature.

Hence such triple points can still lead to undesirable electricalbreakdown in electrical connections between electrical connectors 60.The potentially problematic partial electrical discharge occurs onlywhere there is a relatively high electrical field. The strength of theelectrical field in the electrical connection system is at its greatestat sharp edges in the electrical connector 60. Potting may be used toeliminate the gas pockets 75. However, even using potting insulation maybe insufficient to completely avoid partial electrical discharges atsharp edges where the electrical field strength is high. If theelectrical field strength is great enough, then partial electricaldischarge can result in breakdown of the potting insulation.

As described above, a supply plate 62 that is dimensionally bigger thanthe high voltage supply pad 61 can reduce the effect of triple points inthe electrical connection system. However, it is still possible forrelatively high electrical fields to occur at the points where the highvoltage trace 62 c of the supply plate 62 runs underneath the supply padshield 66.

FIG. 15 depicts an electrical connector 60 in plan view. FIG. 16 depictsthe electrical connector 60 depicted in FIG. 15 in cross-sectional view.The electrical connector depicted in FIGS. 15 and 16 addresses the issueof partial electrical breakdown due to high field strength at theintersection between the edge 132 of the high voltage trace 62 c and theedge 131 of the supply pad shield 66.

In FIG. 15, the dashed lines represent the boundary between the supplyplate 62 and the plate insulator 69. The supply plate 62 and the plateinsulator 69 are disposed in the middle layer of the electricalconnector 60. The boundary between the high voltage supply pad 61 andthe supply pad insulator 68 is shown in a solid line. The boundarybetween the supply pad insulator 68 and the supply pad shield 66 isshown as a solid line.

The electrical connector 60 depicted in FIGS. 15 and 16 is differentfrom the electrical connector 60 depicted in FIGS. 13 and 14 in that theinner edge 131 of the supply pad shield 66 does not cross the outer edge132 of the supply plate 62 perpendicularly. In fact, as depicted inFIGS. 15 and 16, the inner edge 131 of the supply pad shield 66 does notcross the outer edge 132 of the supply plate 62. This is because theinner edge 131 of the supply pad shield 66 lies substantially whollywithin the supply plate 62 when viewed in a direction perpendicular to aplane of the laminate. The supply plate 62 is dimensionally bigger thanthe shape defined by the inner edge 131 of the supply pad shield 66.

As a result of the construction of the electrical connector 60 depictedin FIGS. 15 and 16, the peak electrical field strength of the electricalconnection system is decreased. In particular, the electrical fieldstrength at the inner edge 131 of the supply pad shield 66 is decreased.

This is because electrical breakdown can otherwise take place at theintersection between the outer edge 132 of the high voltage trace 62 cand the inner edge 131 of the supply pad shield 66, which is grounded.This is because both edges 131, 132 can exhibit a relatively highelectrical field strength.

According to the construction depicted in FIGS. 15 and 16, theelectrical field strength at the outer edge 132 of the high voltagetrace 62 c may be high. This is because the electrical field strength isinevitably high at the edge of the conductor at high voltage. However,according to the electrical connector 60 of FIG. 15, the outer edge 132of the high voltage trace 62 c opposes the plane of the supply padshield 66 (rather than the inner edge 131 of the supply pad shield 66).Hence, the electrical field strength at the supply pad shield 66opposing the outer edge 132 of the high voltage trace 62 c is relativelylow.

Hence, the possibility of electrical breakdown is reduced. This isbecause electrical breakdown is more likely to occur at a point in theelectrical connection system where the edges of two conductors are inclose proximity, compared to the edge of one conductor being in closeproximity to the plane of another conductor.

FIG. 17 depicts in plan view an electrical connector 60 according to anembodiment of the invention. In particular, the shape of the supplyplate 62 of the electrical connector depicted in FIG. 17 is differentfrom as described above.

The supply plate 62 depicted in FIG. 17 comprises a portion having agrid pattern. The supply plate 62 is discontinuous in that the supplyplate 62 surrounds several insulating portions 171. Hence, the supplythe plate 62 depicted in FIG. 17 is of a lower density compared to thesupply plate 62 described above.

The purpose of the lower density supply plate 62 of FIG. 17 is toproduce a relatively sparse electrical field when the supply plate 62 isconnected to a high voltage supply. According to the constructionsdepicted in FIG. 17, the electrical field is spread out over a largerarea, thereby decreasing its concentration.

The purpose of the sparse field construction of FIG. 17 is to decreasethe strength of the electrical field at the point at which the edges 132of the high voltage trace 62 c of the supply plate 62 intercept an edge195 of a grounded plane such as the supply pad shield 66. The highvoltage trace 62 c depicted in FIG. 17 comprises a plurality of narrowtraces 62 e. The number of the narrow traces 62 e is not particularlylimited.

In an embodiment, the width of the grid pattern of the high voltagetrace 62 c, which is equal to the combined width of the narrow traces 62e and the insulating portions 171, is approximately five times greaterthan the perpendicular distance between the high voltage trace 62 e andthe grounded plane such as the supply pad shield 66.

FIG. 18 depicts an embodiment of a supply plate 62 of the invention inwhich the narrow traces 62 e take the form of a hatched pattern. Thesupply plate 62 may comprise a portion having a hatched pattern. Thisproduces the sparse electrical field effect that reduces the chance ofelectrical breakdown between the supply plate 62 and the grounded planesuch as the supply pad shield 66.

FIG. 19 depicts in plan view an embodiment of an electrical connector60. The shape of the supply plate 62 of the electrical connector 60depicted in FIG. 19 is different from those described above. The supplyplate 62 comprises a portion in the shape of a spoked wheel. In anembodiment, the spoked wheel portion is substantially coaxial with thehigh voltage supply pad 61 of the electrical connector 60 in plan view.

In FIGS. 19 to 20, the dashed lines represent the boundary between thehigh voltage supply pad 61 and the supply pad insulator 68, as well asthe boundary between the supply pad insulator 68 and the supply padshield 66. The solid lines represent the edge of the supply plate 62,namely the boundary between the supply plate 62 and the plate insulator69.

The spoked wheel reduces the strength of the electrical field at theintersection between the inner edge 131 of the supply pad shield 66 andthe edges 132 of the supply plate 62. The spoked wheel portion of thesupply plate 62 may comprise a plurality of spokes 191 and an outer rim192. The supply plate 62 further comprises a high voltage trace 62 c.

The width of the high voltage trace 62 c may be in the range of fromabout 1 mm to about 4 mm, preferably within the range of from about 1.5mm to about 3 mm and preferably about 2 mm. The width of each spoke 191may be in the range of from about 0.05 mm to about 0.2 mm, preferably inthe range of from about 0.075 mm to about 0.15 mm, and preferably about0.1 mm. The width of the outer rim 192 may be in the range of from about0.5 mm to about 2 mm, preferably in the range of from about 0.75 mm toabout 1.5 mm, and preferably about 1 mm.

In an embodiment, the diameter of the high voltage supply pad 61 is inthe range of from about 1 mm to about 4 mm, preferably in the range offrom about 1.5 mm to about 3 mm, and preferably about 2 mm. In anembodiment, the spoked wheel portion comprises a central hub 193.Preferably, the central hub 193 is coaxial with the high voltage supplypad 61. Preferably, the high voltage supply pad 61 lies substantiallywholly within the central hub 193 of the supply plate 62. In anembodiment, the diameter of the central hub 193 is in the range of fromabout 2 mm to about 4 mm, and preferably about 3 mm.

In an embodiment, the diameter of the region defined by the inner edge131 of the supply pad shield 66 is within the range of from about 2 mmto about 6 mm, preferably in the range of from about 3 mm to about 5 mm,and preferably about 4 mm. In an embodiment, the diameter of the outerrim 192 of the supply plate 62 is within the range of from about 3 mm toabout 9 mm, preferably within the range of from about 4 mm to about 7mm, and preferably about 5 mm.

FIG. 20 depicts an embodiment of an electrical connector 60 in planview. The design of the supply plate 62 of the electrical connector 60depicted in FIG. 20 is different from described above.

The supply plate 62 comprises a wheel portion having spiralling spokes.The wheel portion of the supply plate 62 may comprise a central hub 193,an outer rim 192 and a plurality of spokes 201. The central hub and theouter rim 192 may be as described above in relation to FIG. 19. Thespiralling spokes 201 may have the same width as the spokes 191described in relation to FIG. 19.

The spiralling spokes 201 of FIG. 20 have an edge 202 that interceptswith the inner edge 131 of the supply pad shield 66 at an oblique angle.Here, an oblique angle is taken to mean an angle that is not 90°. Hence,the angle at the intersection between the edge 202 of the spirallingspokes 201 and the inner edge 131 of the supply pad shield 66 is smallerthan the perpendicular angle of FIG. 19.

The purpose of this is to reduce the possibility of electrical breakdownat the intersection between the edges of the supply plate 62 and theinner edge 131 of the supply pad shield 66. It has been observed thatelectrical breakdown is less likely to occur where this angle is low. Inan embodiment, the angle between the edge 132, 202 of the supply plate62 and the intersecting edge 131 of the supply pad shield 66 (in planview) is less than about 70°, preferably less than 45°, more preferablyless than about 30°, and even more preferably less than about 20°.

FIG. 21 depicts in plan view an electrical connector 60. The shape ofthe supply plate 62 is similar to the shape of the supply plate depictedin FIG. 17 except that the narrow traces 62 d extend at an obliqueangle. Accordingly, the angle of interception between the edges 132 ofthe supply plate and the edge 195 of the grounded plane such as thesupply pad shield 66 is oblique.

Preferably, the angle of intersection is less than 70°, more preferablyless than 45°, more preferably less than about 30°, and even morepreferably less than about 20°. Hence, the supply plate 62 comprises aportion having a grid pattern, wherein edges of the supply plateintersecting an edge 195 of the grounded plane such as the supply padshield 66 (in plan view) are at an oblique angle to each other.

FIG. 22 depicts in plan view an electrical connector 60. The supplyplate 62 comprises a meander. The meander coincides with where thesupply plate 62 crosses the edge 195 of the grounded plane such as thesupply pad shield 66. The edge 132 of the supply plate 62 crosses theedge 195 at an oblique angle. In an embodiment the angle is less than orequal to 70°, and preferably approximately 45°.

In an embodiment, the high voltage trace 62 c of the supply plate 62 asdepicted in FIGS. 17, 18, 21 and/or 22 is connect to a high voltagesupply pad 61. In an embodiment, the electrical connector 60 isconnected to an electrostatic clamp 80. Where the electrical connector60 connects to the electrostatic clamp 80, there is a discontinuity inthe supply pad shield 66. The edge 195 of the grounded plane such as thesupply pad shield 66 crosses the high voltage trace 62 c.

1. A high voltage electrical connector comprising a laminate thatcomprises, in order, the following layers: an outer shield layer; anouter insulating layer; a high voltage plate; an inner insulating layer;and a high voltage supply pad; wherein the pad is smaller than the plateand lies substantially wholly within the plate when viewed in adirection perpendicular to a plane of the laminate.
 2. The electricalconnector of claim 2, wherein a minimum distance d between a perimeterof the plate and a perimeter of the pad when viewed in a directionperpendicular to a plane of the laminate is at least h, preferably atleast 2h, preferably by at least 3h, more preferably by least 4h, oreven more preferably by at least 5h, where h is a minimum distancebetween the plate and the pad in the direction perpendicular to theplane of the laminate.
 3. The electrical connector of claim 2, whereinthe plate has a teardrop shape having a substantially circular sectionlarger than the pad such that the pad lies substantially wholly withinthe substantially circular section when viewed in a directionperpendicular to a plane of the laminate, and an extended taperedsection forming an elongated high voltage trace.
 4. The electricalconnector of claim 3, wherein the plate is surrounded in a plane of theplate by a dielectric such that the plate is fully surrounded in a crosssection of the laminate by the dielectric.
 5. The electrical connectorof claim 3, wherein the pad is surrounded in a plane of the pad by a padground shield configured to be connected to electrical ground andwherein the plate is surrounded in a plane of the plate by a plateground shield configured to be connected to electrical ground.
 6. Theelectrical connector of claim 4, wherein the connector further comprisesa ground insulating layer arranged to cover the pad ground shield. 7.The electrical connector of claim 4, wherein a minimum distance betweenthe perimeter of the pad of the connector and the pad ground shield iswithin the range of from about 3h to about 7h, preferably within therange of from about 4h to about 6h, or more preferably about 5h, where his a minimum distance between the plate and the pad in the directionperpendicular to the plane of the laminate.
 8. The electrical connectorof claim 1, wherein at least one of the outer insulating layer, theinner insulating layer, and the ground insulating layer comprisepolyimide.
 9. A high voltage electrical connection system, comprising: afirst electrical connector and a second electrical connector, eachhaving, in order, an outer shield layer, an outer insulating layer, ahigh voltage plate, an inner insulating layer, and a high voltage supplypad, wherein the pad is smaller than the plate and lies substantiallywholly within the plate when viewed in a direction perpendicular to aplane of the laminate; wherein the supply pad of the first electricalconnector is in electrical contact with the supply pad of the secondelectrical connector.
 10. A high voltage electrical connection system,comprising: an electrical connector having, in order, an outer shieldlayer, an outer insulating layer, a high voltage plate, an innerinsulating layer, and a high voltage supply pad, wherein the pad issmaller than the plate and lies substantially wholly within the platewhen viewed in a direction perpendicular to a plane of the laminate; andan electrostatic clamp having a high voltage receipt pad configured toelectrically connect to a component external to the clamp and a highvoltage plate substantially parallel to the pad, wherein the pad issmaller than the plate and lies substantially wholly within the platewhen viewed in a direction perpendicular to a plane of the plate, andwherein the supply pad of the electrical connector is in electricalcontact with the receipt pad of the electrostatic clamp.
 11. Theelectrical connection system of claim 10, wherein at least a portion ofa perimeter of at least one of the pads is in contact with both a gasand an insulator.
 12. The electrical connection system of claim 11,wherein an insulating sheet is interposed between the pads, wherein anelectrical contact extends through the sheet to connect electrically thepads, wherein the contact lies substantially wholly within the pads whenviewed in a direction perpendicular to a plane of the pads, whereinpreferably the contact is a leaf spring, and/or wherein optionally thesheet is made of an elastomer.